1. Field of the Invention
This invention relates to the field of suspensions for disk drives. More particularly, this invention relates to the field of a PZT travel limiter for micro dual stage actuated (DSA) suspensions.
2. Description of Related Art
Disk drive assemblies typically include a voice coil motor (VCM) which mover the suspension in order to position the read/write head on the spinning magnetic disk medium. Dual stage actuated (DSA) suspensions are suspensions that, in addition to the VCM, include at least one actuator mounted somewhere on the suspension itself in order to effect fine positional movements of the read/write head, also called the head slider. Milli-actuators are broadly classified as actuators that move the entire front end of the suspension: spring, load beam, flexure and slider. Micro-actuators are broadly classified as actuators that move only the slider, moving it relative to the load beam, or moving the read-write element only. The actuators are usually piezoelectric devices, though other types of actuators have been proposed and used.
Without admitting that FIG. 1 is “prior art” within the legal meaning of that term, FIG. 1 is a bottom plan view of the area around flexure 20 in a micro DSA suspension 10 according to a prior design by the assignee of the present application. Such a design is generally shown in U.S. Pat. No. 8,879,210 issued to Hahn, which is assigned to the present applicant. In the suspension 10 of FIG. 1, a flexure 20 is mounted to what will be called the bottom side of load beam 14. Load beam or beam portion 14 extends in a generally horizontal direction and supports flexure 20 and read/write head 38 which is mounted to a gimbaled portion 30 of the flexure. Flexure 20 includes a gimbal 24 which supports read/write head 38 in a gimbaled arrangement so that the read/write head pitches and rolls freely in response to surface irregularities in a surface of the spinning data disk as the data disk magnetic media platter surface travels underneath the read/write head. In addition to gimbal 24 which is typically made of a stainless steel support layer, flexure 20 also includes a flexible circuit 34 which includes an insulating layer such as polyimide and a signal conducting layer such as copper or a copper alloy such as copper/beryllium. A bent finger 26 acts as a tongue limiter to limit travel of read/write head 38 during inertial shock events in order to prevent damage to the suspension. Lifter tab 18 is located at the distal end of suspension 20. The “distal” end of a suspension or load beam is the end that is opposite the proximal end, i.e., the “distal” end is the cantilevered end. The “proximal” end of a suspension or load beam is the end that is supported, i.e., the end that is mounted to an actuator arm.
Two piezoelectric actuators 40, sometimes referred to as microactuators, are located on laterally opposite sides of the suspension. Actuators 40 act in push/pull fashion with one actuator typically contracting while the other actuator expands, or vice versa, in order to effect fine movements of read/write head 38 and thereby to position read/write head 38 precisely over the data track desired. For simplicity, the term “PZT” may be used herein as shorthand to refer to the piezoelectric actuators, it being understood that not all piezoelectric actuators comprise lead zirconate titanate (PZT) material. A first and distal end 42 of PZT 40 is affixed to a relatively movable portion of the flexure, in this case specifically to PZT bonding pads or actuator attachment locations 32 which are part of gimbaled portion 30. A second and proximal end 44 of PZT 40 is affixed to a relatively fixed portion of flexure 20 that substantially does not move relative to load beam 10. A small drop of conductive adhesive 46 such as conductive epoxy carries the PZT driving voltage to the metallized top surface of PZT 40 which defines the PZT's top electrode. When PZT 40 expands or contracts in its longitudinal direction in response to a driving voltage, it pushes or pulls on gimbaled portion 30 to rotate that gimbaled portion and thus move read/write head 38. A servo feedback loop keeps read/write head 38 properly positioned over the desired data track on the data disk.
FIG. 2 is a top perspective view of the suspension 10 of FIG. 1. Tongue limiter 26 extends through aperture 16 in load beam 14, and typically includes T-arms 27 which may or may not be bent as shown.